Pete COMMENTS
If true (corroborating intelligence is required) Trump's surprise approval (see Article below) for South Korea (SK) to build nuclear submarines has many implications, including:
- Trump (to maximise US profits) might want Australia and SK to embark on a bidding war to secure scarce US nuclear submarine resources. This includes whole subs, US submarine reactor technology and the very highly enriched (95% U235) weapons' grade uranium that goes into the US reactors. As bidders Australia and SK are very close in Nominal GDP (see Table) hence similar in bidding capability.
- The already high risk AUKUS Pillar 1 agreement for Virginia submarines is more uncertain than up to mid October 2025, when AUKUS Pillar 1 US good faith was taken for granted by the Australian Government. Risks include huge costs, lengthy timelines and inability of the US to build Virginias quickly enough to keep its end of the Virginia sales "by 2032" bargain. In a nutshell the entry of SK's needs and expectations adds uncertainty.
REVISIONS and Additions REDDED
- What does SK say it wants and what does it really want? It seems SK, will pay the multi-$Billion nuclear sub entry fee to the US via construction of a prototype "K-SSN" SK and the US build at Hanwha Ocean's "Philly" [Philadelphia] USA shipyard. So in the medium term (10 years) SK will develop its submarine reactor integration knowledge and experience.
- The K-SSN prototype can be seen as akin the UK's original Dreadnought SSN prototype completed in 1962. SSBN's also rely on SSNs when leaving and entering base. K-SSN could also be useful against any SSBN North Korea (NK) develops and with an outside chance Russia may sell used Delta-class SSBNs to NK.
- What I think SK really wants, in the medium-long term (10-20 years), is to build nuclear ballistic missile armed SSBNs in SK for its first and second strike capability against North Korea. Such a development may be more possible once SK, like Australia, proves itself a source of funding for the US's nuclear sub supply chain. Also SK is greater value than Australia to the US because SK's highly efficient submarine building skills can increase the productivity of the US's slow build submarine industry.
- SK already has ballistic missile submarines in the shape of its KSS-III Batch 1s and 2s. All other ballistic missile subs in the world are nuclear powered because a reactor allows them to stay safely fully submerged and travel at 18 knots for 3 months rather than 3 weeks at 4 knots for SK's current conventional/AIP KSS-IIIs - with predictable needs to run very noisy diesels. So a "K-SSBN" is far less vulnerable than SK's current SSBs. Hence SK logically is also seeking nuclear power/reactors. The Hyunmoo-4.4 SLBMs, probably on the KSS-llls, may have 500km range limitations. But I note SK is developing a much longer range 3,000 kms Hyunmoo-5 land based ballistic missile (IRBM). In land based form it is too heavy and tall, as it must boost a large 8 tonne conventional warhead. But for only a one tonne nuclear warhead a 10m tall Hyunmoo-5 at 1.6m diameter would be a well miniaturized SLBM with perhaps a range of 5,500km. That may be ideal for a KSS-lll SSBs or K-SSBNs to have much safe sea-space to hit NK from afar. Such a missile would be slightly larger than the 1964 Polaris A-3.
Since 2015 I have speculated SK's KSS-III Batch 3 (then called KSSN or KSS-N) subs would be nuclear powered.
Also see my:
2020 article (on SK's request for enriched uranium for submarine reactors from the first Trump administration)
September 2025 article (where I also discuss SK strategic tensions with Japan which might cause Japan to develop a nuclear sub reactor).
Trump's SK surprise also has implications for Canada which has suffered US opposition to Canada purchasing UK or French nuclear submarines for decades. Canada wants superior under ice performance in its future class of subs. Nuclear subs would be ideal. So Canada will be arguing "if it is OK for Australia and SK to have nuclear subs why not us (Canada) as well?" SK could build SSNs for Canada.
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ARTICLE
Japan's NHK World News reports
October 30, 2025 at https://www3.nhk.or.jp/nhkworld/en/news/20251030_06/
"South Korea requests US approval for acquiring
nuclear-powered submarines"
"South Korean
President Lee Jae-myung has asked US President Donald Trump
for approval to acquire nuclear-powered submarines at a summit meeting on
Wednesday.
Trump wrote on [Truth
Social at https://truthsocial.com/@realDonaldTrump/posts/115459650821125830 , on October 30, 2025], "Our Military Alliance is stronger
than ever before and, based on that, I have given them [South Korea]
approval to build a Nuclear Powered Submarine."
The two leaders met in the South Korean city of Gyeongju to discuss tariffs and
North Korea, among other things.
Lee told Trump he hopes the US president will decide
to allow South Korea to acquire fuel supplies for nuclear-powered submarines so
that it can build several such vessels using its own technology.
Lee added that South Korea using nuclear-powered
submarines to defend the waters around the Korean Peninsula would ultimately
reduce the burden on US forces.
South Korea's Yonhap News Agency reported that it is the first time the South Korean
government has made public its intention to acquire nuclear-powered submarines.
The media outlet carried an analysis presuming that
the South Korean request comes as Seoul feels the need to promptly put
nuclear-powered submarines into operational deployment to deal with threats
from Pyongyang [North Korea]."
Dear Pete,
ReplyDeletewhy should anyone keep a submarine 3 months on station if 3 weeks would work? US SSBN would travel alone at least 7 to 10 days to reach station. That's about 3 weeks for the journey itself. South Korea just needs to dip its submarines in the water and they are on station. The deterence is not the boat, it's the missile.
Regards,
MHalblaub
Pete still a lot of unlnowns but I have no doubts about the South Koreans ability or willingness to build or buy SSNs. This tweet suggests they are looking to build their own design of 5000 tonne LEU powered SSN with 10 VLS. They might only need US permission to enrich the LEU. An easier way forward for Australia too?
ReplyDeletehttps://x.com/NavyWor/status/1983750665425056232
As Pete is well aware, I’ve always had the opinion that South Korea has wanted SSBN boats for decades, with North Korea frequently ramping up the tension.
ReplyDeleteThe RoKN do not need SSNs against a North Korean threat, their SSG/SSN (AIP) boats are cutting edge and fully capable for operations against the DPRKN.
A SSBN will enable SK to achieve MAD (Mutually Assured Destruction) against ANY opponent, as an RoKN SSBN could lurk on station in the Pacific for three to six months.
Donald Trump is good at opening his mouth, but he’s often very far from the truth, like his executive order to switch US carriers back to steam catapults, which have not been made since 1996. If he signs this EO, it will restart an entire steam industry that has been dead for thirty years.
Hi MHalblaub at 10/31/2025 9:54 PM
ReplyDelete3 weeks doesn't work for any fully operational SSBNs in the world. When they are coming and going into port they are vulnerable to waiting SSNs and SSKs. When they are on patrol they are safer.
Cheers Pete
That's a problem for Navies with few SSBNs like France or the UK with just 4 submarines and just one out on station. South Korea can afford to build 9 KSS-III. The UK has in total 10 submarines and France 9. South Korea has additional 18 submarines to protect their SSBKs.
DeleteThere was also the need for range on early SSBN due to limited range of the missiles. They had to move close to the enemy. With Trident II the US SSBNs won't need to leave a US harbour to attack. The South Korean submarine launched Hyunmoo-4.4 missile has a range of just 500 km. That is a very limited box for operations reachable with slow speed in 2 or 3 days. I guess leaving Busan is far saver than the rest of the operation. I also guess just one month at sea is far nicer for the crew than a longer duration.
Hi Anonymous at 10/31/2025 11:31 PM
ReplyDeleteThe submarine that SK just launched with 10 VLS is a KSS-III Batch 2 which is an conventionally powered ballistic missile submarine (SSB). See "The design also incorporates ten K-VLS cells" at https://en.wikipedia.org/wiki/Dosan_Ahn_Changho-class_submarine#Batch-II
All these SK nuclear interest issues seem new to most, but not to me. I've been writing about SK's possible interest in the French K15 LEU reactors since 2020. See https://gentleseas.blogspot.com/2020/10/leu-more-acceptable-for-south-korean.html
Cheers Pete
Pete thanks, that article was before I started reading your blog. Very interesting.
DeleteHi Shawn at 11/02/2025 8:51 PM
ReplyDeleteYes I cannot agree more. SK interest in SSBNs is very much an evolution from building the world's only SSBs, called the KSS-IIIs, since 2014 - see https://en.wikipedia.org/wiki/Dosan_Ahn_Changho-class_submarine
Agree that all SK's SSKs are useful against NKs subs until when/if NK produces an SSBN. But building an SSBN might take NK a decade or more, unless it buys used Russian Delta class SSBNs.
https://en.wikipedia.org/wiki/Delta-class_submarine#Delta_IV_(Project_667BDRM_Delfin)_7_boats
SK's small size and close proximity to NK, PRC and Russia make everything but SSBNs vulnerable as a means of Mutually Assured Destruction (MAD)/Deterrence . Indeed an SSBN will enable SK to achieve MAD without any need to build very vulnerable ICBMs/silos or nuclear armed fighter-bombers.
Yes I think Trump has been anti EMALS for years. Hegseth is not qualified to make Trump see sense.
And resuming US nuclear explosion tests anyone?!
Cheers Pete
Hi Anonymous at 11/05/2025 12:52 AM
ReplyDeleteIts true that a total fleet of only 4 SSBNs risks limited availability. Even worse when 1 of the 4 is in unexpected lengthy maintenance - like HMS Vanguard's 7 years https://en.wikipedia.org/wiki/HMS_Vanguard_(S28)#Overhaul_and_refueling .
Once/if SK builds/buys nuclear subs it will have a very powerful Russia/India/China like nuke and conventional submarine mix.
Yes limited range Polaris missiles were why the US based some SSBNs in Guam and Scotland in the 1960s to be closer to Russian targets.
On the Hyunmoo-4.4's range limitations I note SK is developing a much longer range 3,000 kms Hyunmoo-5 - see https://en.wikipedia.org/wiki/Hyunmoo#Hyunmoo-5 . SK is developing a land based Hyunmoo-5 ballistic missile (MRBM). In that form it is too heavy and tall, necessary to boost its 5 tonne warhead.
But for only a one tonne nuclear warhead an 10m tall Hyunmoo-5 at 1.6m diameter would be a well miniaturised SLBM with perhaps a range of 5,500km. Ideal for a K-SSBN to have much safe sea-space to hit NK from afar. Such a weapon would be slightly larger than an improved Polaris A3 https://en.wikipedia.org/wiki/UGM-27_Polaris#Polaris_A-3
Cheers Pete
Thanks Anonymous at 11/06/2025 7:59 PM
ReplyDeleteCheers Pete